20世纪中叶以来AMOC的变化趋势与未来稳定性——进展与展望OA

The Atlantic Meridional Overturning Circulation(AMOC),a key component of the global climate system,behaves as a typical climate tipping element with multi-stable states.Changes in AMOC instigate a series of cascading effects,profoundly affecting distributions of heat and moisture globally.Up till now,due to relatively short durations of direct observations from monitoring arrays(e.g.,RAPID array(21 years)and OSNAP array(11 years)),our understanding of the evolution of the AMOC since the mid-20th century remains highly controversial.Fingerprint reconstructions based on sea-surface temperature and salinity proxies show a marked AMOC weakening since the mid-to-late 20th century,whereas estimates derived from the impacts of circulation intensity changes as well as those based on physical principles—such as ocean-atmosphere heat fluxes or sea surface height gradients—mostly show no significant trend.Additionally,although some metrics may also be able to characterize the AMOC variability,they are generally difficult to robustly assess the long-term trends due to data limitations(e.g.,resolution of sedimentary records and measurement uncertainties)and specific processing methods(e.g.,the detrending applied to sea-level gradient indices).These discrepancies underscore the inherent limitations of different reconstruction methods,and/or the potential masking effects of the natural variability. Regarding future changes in the AMOC,while multi-model ensembles project with high confidence that the AMOC will weaken persistently over the rest of 21st century,the degree of this weakening remains highly uncertain.Furthermore,substantial discrepancies are apparent among different models:although some modeling studies indicate the theoretical existence of a future AMOC tipping point,the timing of such an event in the real climate system remains extremely uncertain.On the other hand,potential negative feedback mechanisms in the climate system could have a stabilizing effect on the AMOC,but this is difficult to assess assuredly.Overall,the most plausible scenario for the future AMOC evolution would be a continued weakening trend,accompanied by an unquantifiable yet non-negligible risk of abrupt transition.To address the knowledge gaps that are critical in the field,such as the outstanding issues concerning potential false positives in early warning signals,the model biases in simulating modern climate processes,and projection biases caused by the missing of key processes including ice-sheet melting,future research should focus on the following priorities.(1)Expand direct observation arrays to enhance the spatiotemporal coverage.(2)Improve climate models,particularly by incorporating ice-sheet processes,to enhance the ability to simulate abrupt climate transitions.(3)Integrate Bayesian statistical frameworks to explicitly incorporate the prior probability for the existence of tipping points and to quantify the risk of abrupt transition through likelihood ratio analysis.(4)Promote research on"past-present analog"in the early warning analysis to understand modern signals in the context of paleoclimate resemblances,thereby improving prediction reliability.(5)Deepen our understanding of the cascades in response to changes in AMOC by reconstructing high-resolution geological records from key regions beyond the North Atlantic,thus providing more evidence for assessing the stability of the climate system.This represents a novel approach to infer AMOC stability through cascading responses to AMOC changes from other climate systems.However,caution is usually required for such an approach,as the coupling could potentially undermine the reliability of early warning signals.(6)Improve machine learning approaches to identify complex nonlinear patterns and early warning signals of AMOC stability from multi-source data,thereby helping to distinguish true critical slowdowns from data-artifact"false positives",predicting rate-induced tipping points under noisy conditions,and identifying underlying physical drivers.These efforts are crucial for reducing uncertainties in future AMOC projections—a vital part of global climate risk assessment.